I bought a cheap oval (well, rounded rectangular really

) one, for the rare occasions when I need such a tool. I'm very happy with it and wouldn't hesitate to buy another one the same, to increase my diffusing/reflecting options, if I planned to do more portraiture.
Having the large dimensions was very handy for me when I tried doing some full length portraits, as it kept the lighting pretty even all down one side of the body (whereas a little round one might only light the face :|).
I also found that the gold side was much too warm, especially if you're reflecting sunlight off it (as opposed to a bare flash). If I had two, I could put the gold one behind the shoot-thru diffuser panel and use it that way, I suppose :shrug:.
Folding it up to put it back into the bag is always fun as well - it's an art that, once mastered, will amaze your friends at parties

!
For what they cost, I'd say, get one and try it

! Then, get another one

.